1. Field of the Invention
The present invention relates to an air conditioning system, and in particular an air conditioning system which includes a thermal storage unit capable of improving heating and defrosting properties.
2. Description of the Related Art
Such an air conditioning system with a thermal storage unit utilizes energy stored in the thermal storage unit at the start of heating, or for defrosting an outdoor heat exchanger during heating, thereby improving air conditioning properties. Such type of conventional air conditioning systems have been disclosed in e.g. Japanese Unexamined Patent Publication No. 21450/1988, Japanese Unexamined Patent Publication No. 38563/1989 and Japanese Unexamined Patent Publication No. 174864/1989.
Referring now to FIG. 4, there is shown a refrigeration cycle of a conventional air conditioning system with a thermal storage unit included therein.
In FIG. 4, reference numeral 1 designates a compressor. Reference numeral 2 designates a four port reversing valve. Reference numeral 3 designates an indoor heat exchanger which functions as a condenser during heating. Reference numeral 4 designates a pressure reducing device. Reference numeral 5 designates a two port bypass valve which bypasses the pressure reducing device 4. Reference numeral 6 designates an outdoor heat exchanger which works as an evaporator during heating. Reference numerals 7 designates a three port valve. Reference numeral 8 and 9 designate a thermal storage heat exchanger and a thermal absorption heat exchanger which are arranged at a lower portion and an upper portion in a thermal storage tank 10, respectively. Reference numeral 8a designates a thermal storage refrigerant inlet which is the refrigerant inlet of the thermal storage heat exchanger 8. Reference numeral 8b designates a thermal storage refrigerant outlet which is the refrigerant outlet of the thermal storage heat exchanger 8. Reference numeral 9a designate a thermal absorption refrigerant inlet which is the refrigerant inlet of the thermal absorption heat exchanger 9. Reference numeral 9b designates a thermal absorption refrigerant outlet which is the refrigerant outlet of the thermal absorption heat exchanger 9. Reference numeral 11 designates a thermal storage material which is filled in the thermal storage tank 10, whose melting point is 40.degree.-60.degree. C., and is made of paraffin or the like.
Now, an operation of the conventional air conditioning system which is constructed as stated above will be explained.
In the case of a heating and thermal storage operation, the two port bypass valve 5 is closed, and the three port valve 7 is switched to communicate with the four port reversing valve 2. A high temperature and high pressure gaseous refrigerant which has been discharged from the compressor 1 heats the thermal storage material 11 in the thermal storage tank 10 when it is passing through the thermal storage heat exchanger 8, and then passes through the four port reversing valve 2. The refrigerant carries out heat exchange with indoor air in the indoor heat exchanger 3 to carry out heating, thereby becoming a normal temperature and high pressure liquid refrigerant. After that, the liquid refrigerant is depressurized by the pressure reducing device 4, is evaporated in the outdoor heat exchanger 6 to become a gaseous refrigerant, and returns to the compressor 1 through the three port valve 7 and the four port valve 2. In this cycle, the thermal storage material 11 is melted due to such heating.
On the other hand, in the case of a defrosting operation which is carried out to eliminate frost deposited on the outdoor heat exchanger 6 during heating when an outdoor temperature is low, the two port bypass valve 5 is opened, and the three port valve 7 is switched to communicate with the thermal absorption heat exchanger 9. The high temperature and high pressure gaseous refrigerant which has been discharged from the compressor 1 heats the thermal storage material 11 in the thermal storage heat exchanger 8, and then passes through the four port reversing valve 2. The refrigerant carries out heat exchange with the indoor air in the indoor heat exchanger 3 to heat it to a limited extent, thereby becoming a two phase high temperature and high pressure refrigerant. After that, the two phase refrigerant passes through the two port bypass valve 5, and reaches the outdoor heat exchanger 6. In the outdoor heat exchanger 6, the refrigerant melts the frost on the surface of the outdoor exchanger, and becomes a low temperature and medium pressure liquid refrigerant. Then the liquid refrigerant passes through the three port valve 7, absorbs heat from the thermal storage material 11 in the thermal absorption heat exchanger 9 to be evaporated into a gaseous refrigerant, and returns to the compressor 1. In this cycle, the thermal storage material 11 is solidified due to such thermal absorption. In that manner, heating can be carried out even during defrosting, thereby preventing an indoor temperature from lowering during defrosting.
In addition, in the case of a heating kick off operation wherein heating can be started in a short and smooth manner when an outdoor temperature is low, the two port bypass valve 5 is opened, and the three port valve 7 is switched to communicate with the thermal absorption heat exchanger 9 like the defrosting operation. The high temperature and high pressure gaseous refrigerant which has been discharged from the compressor 1 heats the thermal storage material in the thermal storage heat exchanger 8, and then passes through the four port reversing valve 2. The refrigerant carries out heat exchange with the indoor air in the indoor heat exchanger 3 to heat it, thereby becoming a high temperature and high pressure liquid refrigerant. The liquid refrigerant passes through the two port bypass valve 5, through the outdoor heat exchanger 6 having the amount of heat exchange restrained to the minimum, and through the three port valve 7. The refrigerant absorbs heat from the thermal storage material 11 in the thermal absorption heat exchanger 9 to be evaporated into a gaseous refrigerant, and returns to the compressor 1. In this cycle, the thermal storage material 11 is solidified due to such thermal absorption. As explained, the refrigerant which returns to the compressor 1 is a high temperature gas. As a result, the efficiency of the compressor can be improved, and heating can be carried out in a rapid and sufficient manner at the start of heating even when the outdoor temperature is low.
By the way, the thermal storage heat exchanger 8 is arranged at the lowest portion in the thermal storage tank 10 so that a melted region of the thermal storage material 11 spreads upward in the thermal storage tank 10 due to convection with the lapse of time. In addition, considering that a raise in temperature of an upper portion of the thermal storage material 11 in the thermal storage tank far from the thermal storage heat exchanger 8 is later than a raise in temperature of a lower portion of the thermal storage material 11 in the thermal storage tank 10, the thermal absorption refrigerant inlet 9a and the thermal absorption refrigerant outlet 9b are arranged at an upper portion and at a lower portion in the thermal storage tank 10, respectively, so that reverse flows are formed between the thermal storage material 11 and the refrigerant in terms of temperature, aiming at obtaining a high level of thermal absorption effect during defrosting or at the start of heating.
Since the conventional air conditioning system is constructed as stated above, when it is impossible to obtain height required for the thermal storage tank 10 due to a limited installation space, not only how to flow the refrigerant at the thermal absorption heat exchanger 9 is limited, but also an installation area has to be widened to ensure a requisite capacity of the thermal storage material 11, which means that the thermal storage heat exchanger 8 at the lowest level has to be prepared in a large size. Making the thermal storage heat exchanger great creates a problem in that the balance between thermal storage and thermal absorption is upset to lower the efficiency of heat exchange.
Japanese Unexamined Patent Publication No. 163741/1988 discloses a solution to solve the problem. By this solution, the flow direction of the refrigerant in the thermal storage heat exchanger is reverse to the flow direction of the refrigerant in the thermal absorption heat exchanger, and a temperature distribution in the thermal storage material as a thermal medium forms a reverse flow to the flow direction of the refrigerant in terms of temperature in both thermal storage and thermal absorption, thereby allowing the thermal storage operation and the thermal absorption operation to be carried out effectively.
However, when thermal storage is made again e.g. immediately after completion of defrosting wherein the thermal storage material has been solidified, heat exchange is abruptly carried out in the vicinity of the thermal storage refrigerant inlet because a temperature difference between the refrigerant gas discharged from the compressor, and the thermal storage material is large. As a result, the temperature of the refrigerant in the vicinity of the thermal storage refrigerant outlet lowers, which brings such state that a raise in temperature of the thermal storage material in the vicinity of the thermal storage refrigerant outlet is later than a raise in temperature of the thermal storage material in the vicinity of the thermal storage refrigerant inlet, causing a non-uniform temperature distribution to be likely to appear in the thermal storage material. Such circumstances prevent the thermal storage material in the vicinity of and above the thermal storage refrigerant outlet from being fully melted in such operation that thermal storage and thermal absorption are repeated with a relatively shorter cycle like the heating operation accompanied by the defrosting operation. This creates a problem in that some portion of the thermal storage material can not be utilized in an effective manner, heating capability lowers during defrosting, the time required for defrosting lengthens, and the heating kick off capability lowers.